U.S. patent application number 14/764002 was filed with the patent office on 2015-12-17 for method and apparatus for configuring random access sequence length for high carrier frequency band in wireless communication system.
This patent application is currently assigned to LG ELECTRONICS INC.. The applicant listed for this patent is LG ELECTRONICS INC.. Invention is credited to Jaehoon CHUNG, Jinmin KIM, Kitae KIM, Hyunsoo KO.
Application Number | 20150365978 14/764002 |
Document ID | / |
Family ID | 51262555 |
Filed Date | 2015-12-17 |
United States Patent
Application |
20150365978 |
Kind Code |
A1 |
KIM; Kitae ; et al. |
December 17, 2015 |
METHOD AND APPARATUS FOR CONFIGURING RANDOM ACCESS SEQUENCE LENGTH
FOR HIGH CARRIER FREQUENCY BAND IN WIRELESS COMMUNICATION
SYSTEM
Abstract
A method of receiving a random access sequence by a base station
in a wireless communication system is disclosed. The method
includes transmitting information on at least one of random access
formats for different effective channel lengths to the user
equipment from a base station, and transmitting a random access
sequence based on the at least one random access format from the
base station, wherein the random access formats have different
lengths of effective channel section for receiving the random
access sequence.
Inventors: |
KIM; Kitae; (Seoul, KR)
; KIM; Jinmin; (Seoul, KR) ; KO; Hyunsoo;
(Seoul, KR) ; CHUNG; Jaehoon; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG ELECTRONICS INC. |
Yeongdeungpo-gu, Seoul |
|
KR |
|
|
Assignee: |
LG ELECTRONICS INC.
Seoul
KR
|
Family ID: |
51262555 |
Appl. No.: |
14/764002 |
Filed: |
January 28, 2014 |
PCT Filed: |
January 28, 2014 |
PCT NO: |
PCT/KR2014/000786 |
371 Date: |
July 28, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61757719 |
Jan 29, 2013 |
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61867140 |
Aug 18, 2013 |
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Current U.S.
Class: |
370/329 |
Current CPC
Class: |
H04J 13/0062 20130101;
H04L 5/0048 20130101; H04L 5/0094 20130101; H04W 74/00 20130101;
H04W 74/0833 20130101; H04W 56/00 20130101; H04W 74/006 20130101;
H04L 27/2613 20130101 |
International
Class: |
H04W 74/08 20060101
H04W074/08; H04J 13/00 20060101 H04J013/00 |
Claims
1. A method for receiving a random access sequence by a base
station in a wireless communication system, the method comprising:
selecting at least one of random access formats for different
effective channel lengths; transmitting information on the at least
one selected random access format to a user equipment; and
receiving a random access sequence based on the at least one
selected random access format from the user equipment, wherein the
random access formats have different lengths of effective channel
section for receiving the random access sequence.
2. The method according to claim 1, wherein the selecting comprises
selecting a random access format for a maximum effective channel
section length when a reception delay value of the user equipment
is equal to or more than a preset value.
3. The method according to claim 1, wherein the selecting comprises
selecting a random access format for a maximum effective channel
section length when the user equipment is an initial access user
equipment.
4. The method according to claim 1, wherein: random access formats
of the different effective channel lengths have different numbers
of supportable user equipments; and a random access format for a
maximum effective channel section length has the supportable user
equipments with a minimum number.
5. The method according to claim 1, wherein a plurality random
access formats are for respective different sequence regions of the
random access sequence when the plural random access formats are
selected from the random access formats.
6. The method according to claim 1, wherein the random access
sequence is a Zadoff-Chu (ZC) sequence.
7. A method of transmitting a random access sequence by a user
equipment in a wireless communication system, the method
comprising: transmitting information on at least one of random
access formats for different effective channel lengths to the user
equipment from a base station; and transmitting a random access
sequence based on the at least one random access format from the
base station, wherein the random access formats have different
lengths of effective channel section for receiving the random
access sequence.
8. The method according to claim 7, wherein the at least one random
access format is a random access format for a maximum effective
channel section length when a reception delay value of the user
equipment is equal to or more than a preset value.
9. The method according to claim 7, wherein the at least one random
access format is a random access format for a maximum effective
channel section length when the user equipment is an initial access
user equipment.
10. The method according to claim 7, wherein: random access formats
of the different effective channel lengths have different numbers
of supportable user equipments; and a random access format for a
maximum effective channel section length has the supportable user
equipments with a minimum number.
11. The method according to claim 7, wherein a plurality random
access formats are for respective different sequence regions of the
random access sequence when information on the plural random access
formats is received from the base station.
12. The method according to claim 7, wherein the random access
sequence is a Zadoff-Chu (ZC) sequence.
Description
TECHNICAL FIELD
[0001] The present invention relates to a wireless communication
system, and more particularly, to a method and apparatus for
configuring a random access sequence length for a high carrier
frequency band in a wireless communication system.
BACKGROUND ART
[0002] A brief description will be given of a 3rd Generation
Partnership Project Long Term Evolution (3GPP LTE) system as an
example of a wireless communication system to which the present
invention can be applied.
[0003] FIG. 1 illustrates a configuration of an Evolved Universal
Mobile Telecommunications System (E-UMTS) network as an exemplary
wireless communication system. The E-UMTS system is an evolution of
the legacy UMTS system and the 3GPP is working on the basics of
E-UMTS standardization. E-UMTS is also called an LTE system. For
details of the technical specifications of UMTS and E-UMTS, refer
to Release 7 and Release 8 of "3rd Generation Partnership Project;
Technical Specification Group Radio Access Network",
respectively.
[0004] Referring to FIG. 1, the E-UMTS system includes a User
Equipment (UE), an evolved Node B (eNode B or eNB), and an Access
Gateway (AG) which is located at an end of an Evolved UMTS
Terrestrial Radio Access Network (E-UTRAN) and connected to an
external network. The eNB may transmit multiple data streams
simultaneously, for broadcast service, multicast service, and/or
unicast service.
[0005] A single eNB manages one or more cells. A cell is set to
operate in one of the bandwidths of 1.4, 3, 5, 10, 15 and 20 MHz
and provides Downlink (DL) or Uplink (UL) transmission service to a
plurality of UEs in the bandwidth. Different cells may be
configured so as to provide-different bandwidths. An eNB controls
data transmission and reception to and from a plurality of UEs.
Regarding DL data, the eNB notifies a particular UE of a
time-frequency area in which the DL data is supposed to be
transmitted, a coding scheme, a data size, Hybrid Automatic Repeat
reQuest (HARQ) information, etc. by transmitting DL scheduling
information to the UE. Regarding UL data, the eNB notifies a
particular UE of a time-frequency area in which the UE can transmit
data, a coding scheme, a data size, HARQ information, etc. by
transmitting UL scheduling information to the UE. An interface for
transmitting user traffic or control traffic may be defined between
eNBs. A Core Network (CN) may include an AG and a network node for
user registration of UEs. The AG manages the mobility of UEs on a
Tracking Area (TA) basis. A TA includes a plurality of cells.
[0006] While the development stage of wireless communication
technology has reached LTE based on Wideband Code Division Multiple
Access (WCDMA), the demands and expectation of users and service
providers are increasing. Considering that other radio access
technologies are under development, a new technological evolution
is required to achieve future competitiveness. Specifically, cost
reduction per bit, increased service availability, flexible use of
frequency bands, a simplified structure, an open interface,
appropriate power consumption of UEs, etc. are required.
DISCLOSURE
Technical Problem
[0007] An object of the present invention devised to solve the
problem lies on a method and apparatus for configuring a random
access sequence length for a high carrier frequency band in a
wireless communication system.
Technical Solution
[0008] The object of the present invention can be achieved by
providing a method for receiving a random access sequence by a base
station in a wireless communication system, the method including
selecting at least one of random access formats for different
effective channel lengths, transmitting information on the at least
one selected random access format to a user equipment, and
receiving a random access sequence based on the at least one
selected random access format from the user equipment, wherein the
random access formats have different lengths of effective channel
section for receiving the random access sequence. The random access
sequence may be a Zadoff-Chu (ZC) sequence.
[0009] Here, the selecting may include selecting a random access
format for a maximum effective channel section length when a
reception delay value of the user equipment is equal to or more
than a preset value. Alternatively, the selecting may include
selecting a random access format for a maximum effective channel
section length when the user equipment is an initial access user
equipment.
[0010] In addition, a plurality random access formats may be for
respective different sequence regions of the random access sequence
when the plural random access formats are selected from the random
access formats.
[0011] In another aspect of the present invention, provided herein
is a method of transmitting a random access sequence by a user
equipment in a wireless communication system, the method including
transmitting information on at least one of random access formats
for different effective channel lengths to the user equipment from
a base station, and transmitting a random access sequence based on
the at least one random access format from the base station, the
random access formats have different lengths of effective channel
section for receiving the random access sequence. The random access
sequence may be a Zadoff-Chu (ZC) sequence.
[0012] Here, the at least one random access format may be a random
access format for a maximum effective channel section length when a
reception delay value of the user equipment is equal to or more
than a preset value. Alternatively, the at least one random access
format may be a random access format for a maximum effective
channel section length when the user equipment is an initial access
user equipment.
[0013] In addition, a plurality random access formats may be for
respective different sequence regions of the random access sequence
when information on the plural random access formats is received
from the base station.
[0014] Random access formats of the different effective channel
lengths may have different numbers of supportable user equipments,
and a random access format for a maximum effective channel section
length may have the supportable user equipments with a minimum
number.
Advantageous Effects
[0015] According to embodiments of the present invention, a user
equipment may effectively transmit a random access sequence in a
wireless communication system.
[0016] It will be appreciated by persons skilled in the art that
that the effects that could be achieved with the present invention
are not limited to what has been particularly described hereinabove
and other advantages of the present invention will be more clearly
understood from the following detailed description taken in
conjunction with the accompanying drawings.
DESCRIPTION OF DRAWINGS
[0017] The accompanying drawings, which are included to provide a
further understanding of the invention, illustrate embodiments of
the invention and together with the description serve to explain
the principle of the invention.
[0018] In the drawings:
[0019] FIG. 1 illustrates a configuration of an Evolved Universal
Mobile Telecommunications System (E-UMTS) network as an example of
a wireless communication system;
[0020] FIG. 2 illustrates a control-plane protocol stack and a
user-plane protocol stack in a radio interface protocol
architecture conforming to a 3rd Generation Partnership Project
(3GPP) radio access network standard between a User Equipment (UE)
and an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN);
[0021] FIG. 3 illustrates physical channels and a general signal
transmission method using the physical channels in a 3GPP
system;
[0022] FIG. 4 illustrates a structure of a downlink radio frame in
a Long Term Evolution (LTE) system;
[0023] FIG. 5 illustrates a structure of an uplink subframe in the
LTE system;
[0024] FIG. 6 illustrates the concept of a small cell, which is
expected to be introduced to the LTE system;
[0025] FIG. 7 illustrates a structure of a Random Access Channel
(RACH) preamble;
[0026] FIG. 8 illustrates an exemplary setting of a Cyclic Prefix
(CP) and a transmission period for an RACH preamble to transmit the
RACH preamble in a high carrier frequency;
[0027] FIG. 9 illustrates another exemplary setting of a CP and a
transmission period for an RACH preamble to transmit the RACH
preamble in a high carrier frequency;
[0028] FIG. 10 is a graph illustrating RACH sequence length versus
service coverage in the LTE system;
[0029] FIG. 11 is a graph illustrating RACH sequence length versus
service coverage in a high carrier frequency system;
[0030] FIG. 12 illustrates the concept of an RACH allocated to a
partial band and configuration of guard bands;
[0031] FIG. 13 illustrates the concept of an effective single path
due to small .DELTA.f.sub.RA and sequence reception of a BS;
[0032] FIG. 14 illustrates the concept of an effective single path
due to great .DELTA.f.sub.RA and sequence reception of a BS;
[0033] FIG. 15 illustrates a cyclic shift principle using a
Zadoff-Chu (ZC) sequence;
[0034] FIG. 16 illustrates the concept of allocation of a multiple
user sequence using cyclic shift;
[0035] FIG. 17 illustrates an example of user detection in
different zero-correlation zones;
[0036] FIG. 18 illustrates an example of configuration of a
zero-correlation zone in consideration of an effective channel
section L according to an embodiment of the present invention;
[0037] FIG. 19 illustrates sequence overlapping that occurs when an
effective channel section L is not considered;
[0038] FIG. 20 illustrates an example of configuration of
zero-correlation zone where sequence overlapping does not occur in
consideration of the effective channel section L;
[0039] FIG. 21 illustrates an example in which the same ZC sequence
is designed in Format #1 and Format #2; and
[0040] FIG. 22 is a block diagram of a communication apparatus
according to an embodiment of the present invention.
BEST MODE
[0041] The configuration, operation, and other features of the
present invention will readily be understood with embodiments of
the present invention described with reference to the attached
drawings. Embodiments of the present invention as set forth herein
are examples in which the technical features of the present
invention are applied to a 3rd Generation Partnership Project
(3GPP) system.
[0042] While embodiments of the present invention are described in
the context of Long Term Evolution (LTE) and LTE-Advanced (LTE-A)
systems, they are purely exemplary. Therefore, the embodiments of
the present invention are applicable to any other communication
system as long as the above definitions are valid for the
communication system. In addition, while the embodiments of the
present invention are described in the context of Frequency
Division Duplexing (FDD), they are also readily applicable to
Half-FDD (H-FDD) or Time Division Duplexing (TDD) with some
modifications.
[0043] FIG. 2 illustrates control-plane and user-plane protocol
stacks in a radio interface protocol architecture conforming to a
3GPP wireless access network standard between a User Equipment (UE)
and an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN). The
control plane is a path in which the UE and the E-UTRAN transmit
control messages to manage calls, and the user plane is a path in
which data generated from an application layer, for example, voice
data or Internet packet data is transmitted.
[0044] A PHYsical (PHY) layer at Layer 1 (L1) provides information
transfer service to its higher layer, a Medium Access Control (MAC)
layer. The PHY layer is connected to the MAC layer via transport
channels. The transport channels deliver data between the MAC layer
and the PHY layer. Data is transmitted on physical channels between
the PHY layers of a transmitter and a receiver. The physical
channels use time and frequency as radio resources. Specifically,
the physical channels are modulated in Orthogonal Frequency
Division Multiple Access (OFDMA) for downlink and in Single Carrier
Frequency Division Multiple Access (SC-FDMA) for uplink.
[0045] The MAC layer at Layer 2 (L2) provides service to its higher
layer, a Radio Link Control (RLC) layer via logical channels. The
RLC layer at L2 supports reliable data transmission. RLC
functionality may be implemented in a function block of the MAC
layer. A Packet Data Convergence Protocol (PDCP) layer at L2
performs header compression to reduce the amount of unnecessary
control information and thus efficiently transmit Internet Protocol
(IP) packets such as IP version 4 (IPv4) or IP version 6 (IPv6)
packets via an air interface having a narrow bandwidth.
[0046] A Radio Resource Control (RRC) layer at the lowest part of
Layer 3 (or L3) is defined only on the control plane. The RRC layer
controls logical channels, transport channels, and physical
channels in relation to configuration, reconfiguration, and release
of Radio Bearers (RBs). An RB refers to a service provided at L2,
for data transmission between the UE and the E-UTRAN. For this
purpose, the RRC layers of the UE and the E-UTRAN exchange RRC
messages with each other. If an RRC connection is established
between the UE and the E-UTRAN, the UE is in RRC Connected mode and
otherwise, the UE is in RRC Idle mode. A Non-Access Stratum (NAS)
layer above the RRC layer performs functions including session
management and mobility management.
[0047] A cell covered by an eNB is set to one of the bandwidths of
1.4, 3, 5, 10, 15, and 20 MHz and provides downlink or uplink
transmission service in the bandwidth to a plurality of UEs.
Different cells may be set to provide different bandwidths.
[0048] Downlink transport channels used to deliver data from the
E-UTRAN to UEs include a Broadcast Channel (BCH) carrying system
information, a Paging Channel (PCH) carrying a paging message, and
a Shared Channel (SCH) carrying user traffic or a control message.
Downlink multicast traffic or control messages or downlink
broadcast traffic or control messages may be transmitted on a
downlink SCH or a separately defined downlink Multicast Channel
(MCH). Uplink transport channels used to deliver data from a UE to
the E-UTRAN include a Random Access Channel (RACH) carrying an
initial control message and an uplink SCH carrying user traffic or
a control message. Logical channels that are defined above
transport channels and mapped to the transport channels include a
Broadcast Control Channel (BCCH), a Paging Control Channel (PCCH),
a Common Control Channel (CCCH), a Multicast Control Channel
(MCCH), a Multicast Traffic Channel (MTCH), etc.
[0049] FIG. 3 illustrates physical channels and a general method
for transmitting signals on the physical channels in the 3GPP
system.
[0050] Referring to FIG. 3, when a UE is powered on or enters a new
cell, the UE performs initial cell search (S301). The initial cell
search involves acquisition of synchronization to an eNB.
Specifically, the UE synchronizes its timing to the eNB and
acquires a cell Identifier (ID) and other information by receiving
a Primary Synchronization Channel (P-SCH) and a Secondary
Synchronization Channel (S-SCH) from the eNB. Then the UE may
acquire information broadcast in the cell by receiving a Physical
Broadcast Channel (PBCH) from the eNB. During the initial cell
search, the UE may monitor a downlink channel state by receiving a
DownLink Reference Signal (DL RS).
[0051] After the initial cell search, the UE may acquire detailed
system information by receiving a Physical Downlink Control Channel
(PDCCH) and receiving a Physical Downlink Shared Channel (PDSCH)
based on information included in the PDCCH (S302).
[0052] If the UE initially accesses the eNB or has no radio
resources for signal transmission to the eNB, the UE may perform a
random access procedure with the eNB (S303 to S306). In the random
access procedure, the UE may transmit a predetermined sequence as a
preamble on a Physical Random Access Channel (PRACH) (S303 and
S305) and may receive a response message to the preamble on a PDCCH
and a PDSCH associated with the PDCCH (S304 and S306). In case of a
contention-based RACH, the UE may additionally perform a contention
resolution procedure.
[0053] After the above procedure, the UE may receive a PDCCH and/or
a PDSCH from the eNB (S307 and transmit a Physical Uplink Shared
Channel (PUSCH) and/or a Physical Uplink Control Channel (PUCCH) to
the eNB (S308), which is a general downlink and uplink signal
transmission procedure. Particularly, the UE receives Downlink
Control Information (DCI) on a PDCCH. Herein, the DCI includes
control information such as resource allocation information for the
UE. Different DCI formats are defined according to different usages
of DCI.
[0054] Control information that the UE transmits to the eNB on the
uplink or receives from the eNB on the downlink includes a DL/UL
ACKnowledgment/Negative ACKnowledgment (ACK/NACK) signal, a Channel
Quality Indicator (CQI), a Precoding Matrix Index (PMI), a Rank
Indicator (RI), etc. In the 3GPP LTE system, the UE may transmit
control information such as a CQI, a PMI, an RI, etc. on a PUSCH
and/or a PUCCH.
[0055] FIG. 4 illustrates exemplary control channels included in
the control region of a subframe in a DL radio frame.
[0056] Referring to FIG. 4, a subframe includes 14 OFDM symbols.
The first one to three OFDM symbols of a subframe are used for a
control region and the other 13 to 11 OFDM symbols are used for a
data region according to a subframe configuration. In FIG. 4,
reference characters R1 to R4 denote RSs or pilot signals for
antenna 0 to antenna 3. RSs are allocated in a predetermined
pattern in a subframe irrespective of the control region and the
data region. A control channel is allocated to non-RS resources in
the control region and a traffic channel is also allocated to
non-RS resources in the data region. Control channels allocated to
the control region include a Physical Control Format Indicator
Channel (PCFICH), a Physical Hybrid-ARQ Indicator Channel (PHICH),
a Physical Downlink Control Channel (PDCCH), etc.
[0057] The PCFICH is a physical control format indicator channel
carrying information about the number of OFDM symbols used for
PDCCHs in each subframe. The PCFICH is located in the first OFDM
symbol of a subframe and configured with priority over the PHICH
and the PDCCH. The PCFICH is composed of 4 Resource Element Groups
(REGs), each REG being distributed to the control region based on a
cell Identity (ID). One REG includes 4 Resource Elements (REs). An
RE is a minimum physical resource defined by one subcarrier by one
OFDM symbol. The PCFICH indicates 1 to 3 or 2 to 4 according to a
bandwidth. The PCFICH is modulated in Quadrature Phase Shift Keying
(QPSK).
[0058] The PHICH is a physical Hybrid-Automatic Repeat and request
(HARQ) indicator channel carrying an HARQ ACK/NACK for an uplink
transmission. That is, the PHICH is a channel that delivers DL
ACK/NACK information for UL HARQ. The PHICH includes one REG and is
scrambled cell-specifically. An ACK/NACK is indicated in one bit
and modulated in Binary Phase Shift Keying (BPSK). The modulated
ACK/NACK is spread with a Spreading Factor (SF) of 2 or 4. A
plurality of PHICHs mapped to the same resources form a PHICH
group. The number of PHICHs multiplexed into a PHICH group is
determined according to the number of spreading codes. A PHICH
(group) is repeated three times to obtain a diversity gain in the
frequency domain and/or the time domain.
[0059] The PDCCH is a physical downlink control channel allocated
to the first n OFDM symbols of a subframe. Herein, n is 1 or a
larger integer indicated by the PCFICH. The PDCCH is composed of
one or more CCEs. The PDCCH carries resource allocation information
about transport channels, PCH and DL-SCH, an uplink scheduling
grant, and HARQ information to each UE or UE group. The PCH and the
DL-SCH are transmitted on a PDSCH. Therefore, an eNB and a UE
transmit and receive data usually on the PDSCH, except for specific
control information or specific service data.
[0060] Information indicating one or more UEs to receive PDSCH data
and information indicating how the UEs are supposed to receive and
decode the PDSCH data are delivered on a PDCCH. For example, on the
assumption that the Cyclic Redundancy Check (CRC) of a specific
PDCCH is masked by Radio Network Temporary Identity (RNTI) "A" and
information about data transmitted in radio resources (e.g. at a
frequency position) "B" based on transport format information (e.g.
a transport block size, a modulation scheme, coding information,
etc.) "C" is transmitted in a specific subframe, a UE within a cell
monitors, that is, blind-decodes a PDCCH using its RNTI information
in a search space. If one or more UEs have RNTI "A", these UEs
receive the PDCCH and receive a PDSCH indicated by "B" and "C"
based on information of the received PDCCH.
[0061] FIG. 5 illustrates a structure of a UL subframe in the LTE
system.
[0062] Referring to FIG. 5, a UL subframe may be divided into a
control region and a data region. A Physical Uplink Control Channel
(PUCCH) including Uplink Control Information (UCI) is allocated to
the control region and a Physical uplink Shared Channel (PUSCH)
including user data is allocated to the data region. The middle of
the subframe is allocated to the PUSCH, while both sides of the
data region in the frequency domain are allocated to the PUCCH.
Control information transmitted on the PUCCH may include an HARQ
ACK/NACK, a CQI representing a downlink channel state, an RI for
Multiple Input Multiple Output (MIMO), a Scheduling Request (SR)
requesting UL resource allocation. A PUCCH for one UE occupies one
Resource Block (RB) in each slot of a subframe. That is, the two
RBs allocated to the PUCCH frequency-hop over the slot boundary of
the subframe. Particularly, PUCCHs with m=0, m=1, and m=2 are
allocated to a subframe in FIG. 5.
[0063] Introduction of local areas to the LTE system in the future
is under consideration. To reinforce service support per user, it
is expected that a new cell will be deployed based on the concept
of local area access.
[0064] FIG. 6 illustrates the concept of a small cell, which is
expected to be introduced to the LTE system.
[0065] Referring to FIG. 6, it is expected that a wider system
bandwidth is set in a frequency band having a higher center
frequency, not in a frequency band used in the legacy LTE system.
Basic cell coverage may be supported based on a control signal such
as system information in an existing cellular frequency band,
whereas data may be transmitted with maximum transmission
efficiency in a wider frequency band in a high-frequency small
cell. Thus, the concept of local area access targets at UEs with
low-to-medium mobility in a small area and small cells will be
deployed, each having a distance between a Base Station (BS) and a
UE in units of 100 m, smaller than existing cells having distances
between a UE and a BS in units of km.
[0066] Due to shorter distances between UEs and a BS and the use of
a high carrier frequency, these small cells may have the following
channel characteristics.
[0067] First of all, from the perspective of delay spread, as the
distance between a BS and a UE is shorter, a signal delay may be
also shorter. If the same OFDM-based frame as used in the LTE
system is adopted, a subcarrier spacing may be set to an extremely
large value, for example, a value larger than the existing
subcarrier spacing 15 kHz because a relatively wide frequency band
is allocated. A Doppler's frequency is higher in a high frequency
band than in a low frequency band, for the same UE speed.
Therefore, a coherence time may be extremely short. The coherence
time is the time over which a channel has static or uniform
characteristics. A coherent bandwidth is a bandwidth in which a
channel has static or uniform characteristics in time.
[0068] Only when a UE is synchronized with a BS, the UE may
transmit a UL signal and may be scheduled for data transmission. A
main role of an RACH is radio access in a transmission scheme that
makes asynchronous UEs orthogonal to one another or prevents
coincident accesses of the UEs as much as possible. The RACH will
be described in greater detail.
[0069] Regarding the usage and requirements of the RACH, a main
function of the RACH is UL initial access and short message
transmission. Although initial network access and short message
transmission take place on the RACH in a Wideband Code Division
Multiple Access (WCDMA) system, short message transmission is not
performed through the RACH in the LTE system. In addition, the RACH
is transmitted separately from an existing UL data channel in the
LTE system, compared to the WCDMA system. That is, while a UL data
channel, PUSCH has a symbol structure with a basic subcarrier
spacing .DELTA.f set to 15 kHz, the RACH has an SC-FDMA structure
with a subcarrier spacing .DELTA.f.sub.RA set to 1.25 kHz. Once UL
synchronization is acquired between a BS and a UE, the UE is
scheduled for orthogonal resource allocation and transmission in
the LTE system.
[0070] The structure of an RACH preamble will be described below.
FIG. 7 illustrates a structure of an RACH preamble.
[0071] Referring to FIG. 7, an RACH preamble includes a Cyclic
Prefix (CP), a preamble sequence, and a Guard Time (GT). The CP is
used to compensate for a maximum channel delay spread and a Round
Trip Time (RTT), and the GT is used to compensate for the RTT. The
CP is a copy of the last part of an OFDM symbol, inserted into the
CP period of the preamble.
[0072] On the assumption that it has been synchronized with a BS, a
UE transmits an RACH preamble to the BS. If the UE is near to the
BS, the BS receives the RACH almost in alignment with a subframe
boundary. On the other hand, if the UE is remote from the BS, for
example, the UE is at a cell edge, the BS receives the RACH later
than a nearby UE's RACH due to a propagation delay. Because the BS
has knowledge of a preamble sequence transmitted by each UE, the BS
may perform a synchronization process based on the detected
position of the preamble transmitted by each UE.
[0073] Many sequences are available for an RACH preamble. For
example, a Zadoff-Chu (ZC) sequence based on auto-correlation and a
pseudorandom sequence based on cross-correlation are popular. In
general, the ZC sequence based on auto-correlation may be selected
in a low intra-cell interference environment and the pseudorandom
sequence based on cross-correlation may be selected in a high
intra-cell interference environment.
[0074] In the LTE system, 1) the intra-cell interference between
different preambles using the same time-frequency RACH resources
should be low; 2) since detection performance increases with the
use of more orthogonal preambles, the detection performance of a BS
should be increased by defining more orthogonal preambles for a
smaller cell; 3) the detection complexity of the BS should be
reduced; and 4) a fast UE should also be supported. To meet the
above requirements, the LTE system uses a ZC sequence of length 839
expressed as [Equation 1], for an RACH preamble.
x u ( n ) = - j .pi. un ( n + 1 ) N zc , 0 .ltoreq. n .ltoreq. N zc
- 1 ( N zc = 839 ) [ Equation 1 ] ##EQU00001##
[0075] However, if the intra-cell interference is high, a
pseudorandom sequence expressed as [Equation 2] may be used for an
RACH preamble.
x.sub.1(n+31)=(x.sub.1(n+3)+x.sub.1(n))mod 2
x.sub.2(n+31)=(x.sub.2(n+3)+x.sub.2(n+2)+x.sub.2(n+1)+x.sub.2(n))mod2
c(n)=(x.sub.1(n+N.sub.c)+x.sub.2(n+N.sub.c))mod2 [Equation 2]
[0076] Now, a description will be given of a transmission bandwidth
for an RACH preamble. Two main factors taken into account in
setting an RACH bandwidth are diversity gain and restriction of UE
transmission power. Since a UE has limited power amplifier
performance relative to a BS, energy per resource unit is decreased
but frequency diversity is maximized by transmitting an RACH in a
wide frequency band. On the contrary, if an RACH preamble is
transmitted in a narrow frequency band, energy per resource unit is
increased but frequency diversity is minimized.
[0077] When an LTE RACH transmission bandwidth is determined
actually, 1.08 MHz, 2.16 MHz, 4.5 MHz, and 50 MHz (having 6 RBs, 12
RBs, 25 RBs, and 50 RBs, respectively) are candidates. Since it is
revealed from a comparison of RACH non-detection probabilities that
6 RBs is enough to satisfy a non-detection probability of 1%, 1.08
MHz is determined as a final RACH transmission bandwidth.
[0078] The length of an RACH preamble sequence will be described
now. To determine the length T.sub.SEQ of an RACH preamble
sequence, conditions for the low and upper bounds of the sequence
length T.sub.SEQ and a subcarrier spacing should be satisfied.
[0079] The lower bound of the sequence length T.sub.SEQ should be
larger than the sum of the RTT and maximum channel delay spread of
a cell-edge UE within coverage in order to eliminate detection
ambiguity. That is, [Equation 3] should be satisfied.
[ Equation 3 ] T SEQ .gtoreq. 2 d long 3 .times. 10 8 + .tau. max
condition #1 ##EQU00002##
[0080] In [Equation 3], d.sub.long represents the service coverage
and .tau..sub.max represents the maximum channel delay spread. For
example, it is assumed that the largest cell has a radius of 100 km
and the maximum channel delay spread of the cell is 16.67 .mu.s in
the LTE system. It is also assumed that service coverage in a high
carrier frequency is 3 km and the maximum channel delay spread of
the high carrier frequency is 0.5 .mu.s. On these assumptions, the
following [Equation 4] and [Equation 5] are given.
T SEQ .gtoreq. 2 100 km 3 .times. 10 8 + 16.67 us = 683.33 us - LTE
case [ Equation 4 ] T SEQ .gtoreq. 2 3 km 3 .times. 10 8 + 0.5 us =
40.5 us - High carrier frequency case [ Equation 5 ]
##EQU00003##
[0081] If the upper bound of the sequence length T.sub.SEQ is
determined in conformance to a general frame standard, the upper
bound cannot exceed a given Transmission Time Interval (TTI). If a
subframe is lms long as in the LTE system, the TTI is 1 ms. Herein,
a maximum sequence period is based on the assumption of service
coverage in which a UE is nearest to a BS and the maximum channel
delay spread is 0 .mu.s. Accordingly, condition #2 expressed as
[Equation 6] should be satisfied.
[ Equation 6 ] T SEQ .ltoreq. TTI - 2 .times. 2 d short 3 .times.
10 8 Condition #2 ##EQU00004##
[0082] In [Equation 6], d.sub.short represents the service coverage
in which a UE is nearest to a BS. For example, d.sub.short is 14.4
km in the LTE system and d.sub.short is 1 km in the high carrier
frequency. If the TTI is 222 ms in the high carrier frequency,
[Equation 7] and [Equation 8] are resulted.
T SEQ .ltoreq. 1 ms - 2 .times. 2 14.4 km 3 .times. 10 8 = 813 us -
LTE case [ Equation 7 ] T SEQ .ltoreq. 222 ms - 2 .times. 2.1 km 3
.times. 10 8 = 208.3 us - High carrier frequency case [ Equation 8
] ##EQU00005##
[0083] Finally, a requirement for the RACH subcarrier spacing
.DELTA.f.sub.RA will be described below.
[0084] If a sampling frequency N.sub.DFT being the reciprocal of
the sequence length T.sub.SEQ is in the relationship that
N.sub.DFT=f.sub.sT.sub.SEQ maximum orthogonality is ensured between
UL subcarriers of an existing frame and RACH subcarriers. Because
the subcarrier spacing .DELTA.f of the existing frame should be an
integer multiple of the RACH subcarrier spacing .DELTA.f.sub.RA,
condition #3 given as [Equation 9] should be satisfied.
[ Equation 9 ] .DELTA. f RA = f s N DFT = 1 T SEQ = 1 k T SYM =
.DELTA. f k Condition #3 ##EQU00006##
[0085] In this case, the RACH subcarrier spacing .DELTA.f.sub.RA is
determined in the LTE system by the following equation.
.DELTA. f RA = 30.72 MHz 2048 = 1 800 us = 1 12 66.67 us = 15 kHz
12 = 1.25 kHz [ Equation 10 ] ##EQU00007##
[0086] Hereinbelow, an exemplary setting of an RACH preamble period
for RACH transmission in a high carrier frequency, satisfying
condition #1, condition #2, and condition #3 will be described. For
a minimum service coverage of 1 km and a maximum service coverage
of 3 km, an RTT is calculated and a maximum channel delay spread of
0.5 .mu.s is considered.
TABLE-US-00001 TABLE 1 TTI - (GP + CP) RTT CP for RACH GP + TTI
Sequence Coverage (GP) (RTT + 0.5 us) CP candidate duration 1
km(short) 6.6 us 7.1 us 13.7 us 222 us 208.3 us 767 us 754.3 us 125
us 111.3 us 3 km(long) 20.0 us 20.5 us 40.5 us 222 us 181.9 us 767
us 726.9 us 125 us 84.9 us
[0087] If the service coverage is 3 km and the TTI is 222 .mu.s, an
RACH preamble period and a CP are calculated by [Table 2].
TABLE-US-00002 TABLE 2 k = .DELTA.f/.DELTA.f.sub.RA = 18 .ltoreq.
.left brkt-bot.T.sub.SEQ/T.sub.SYM.right brkt-bot. = .left
brkt-bot.181.9 us/(1/104.25 kHz).right brkt-bot. = 18
.DELTA.f.sub.RA = .DELTA.f/k = 104.24 kHz/18 = 5.7917 kHz T.sub.SEQ
= 1/.DELTA.f.sub.RA = 172.66 us T.sub.CP = 20.5 us
[0088] As noted from [Table 3] below, condition #1, condition #2,
and condition #3 are all satisfied with the calculated sequence
length T.sub.SEQ=172.66 us.
TABLE-US-00003 TABLE 3 Condition #1 : T SEQ = 172.66 us .gtoreq. 2
3 km 3 .times. 10 8 + 0.5 us = 40.5 us ##EQU00008## Condition #2 :
T SEQ = 172.66 us .ltoreq. 222 ms - 2 .times. 2 3 km 3 .times. 10 8
= 181.9 us ##EQU00009## Condition #3: .DELTA.f.sub.RA = .DELTA.f/k
= 104.24 kHz/18 = 5.7917 kHz
[0089] Therefore, a final RACH preamble may be configured as
illustrated in FIG. 8. FIG. 8 illustrates an exemplary setting of a
CP and a transmission period for an RACH preamble, for RACH
preamble transmission in a high carrier frequency. In the
illustrated case of FIG. 8, the service coverage is 3 km and the
TTI is 222 .mu.s.
[0090] In another example, if the service coverage is 1 km and the
TTI is 125 .mu.s, the values illustrated in [Table 4] may be
calculated.
TABLE-US-00004 TABLE 4 k = .DELTA.f/.DELTA.f.sub.RA = 12 .ltoreq.
.left brkt-bot.T.sub.SEQ/T.sub.SYM.right brkt-bot. = .left
brkt-bot.111.3 us/(1/120 kHz).right brkt-bot. = 13 .DELTA.f.sub.RA
= .DELTA.f/k = 120 kHz/12 = 10 kHz T.sub.SEQ = 1/.DELTA.f.sub.RA =
100 us T.sub.CP = 7.1 us
[0091] As noted from [Table 5] below, condition #1, condition #2,
and condition #3 are all satisfied with the calculated sequence
length T.sub.SEQ=100 us.
TABLE-US-00005 TABLE 5 Condition #1 : T SEQ = 100 us .gtoreq. 2 1
km 3 .times. 10 8 + 0.5 us = 7.1 us ##EQU00010## Condition #2 : T
SEQ = 100 us .ltoreq. 125 ms - 2 .times. 2 1 km 3 .times. 10 8 =
111.3 us ##EQU00011## Condition #3: .DELTA.f.sub.RA = .DELTA.f/k =
120 kHz/12 = 10 kHz
[0092] Therefore, a final RACH preamble may be configured as
illustrated in FIG. 9. FIG. 9 illustrates another exemplary setting
of a CP and a transmission period for an RACH preamble, for RACH
preamble transmission in a high carrier frequency. In the
illustrated case of FIG. 9, the service coverage is 1 km and the
TTI is 125 .mu.s.
[0093] To verify whether a target area of a sequence satisfying
condition #1, condition #2, and condition #3 is appropriately
designed, link budget parameters listed in [Table 6] may be
used.
TABLE-US-00006 TABLE 6 Parameter LTE value Higher Carrier Band
Carrier frequency(f.sub.c) 2 GMHz 30 GHz eNB antenna
height(h.sub.b) 30 m/60 m 10 m(3 GPP 36.814 UMI) UE antenna
height(h.sub.m) 1.5 m 1.5 m UE transmit Power(P.sub.max, 24 dBm(250
mW) 24 dBm EIRP) eNB receiver Ant. Gain 14 dBi 14 dBi (G.sub.a)
Receiving Noise 5 dB 5 dB Figure(N.sub.f) Thermal Noise -174 dBm/Hz
-174 dBm/Hz Density(N.sub.0) Required (E.sub.p/N.sub.0) 18 dB 18 dB
Penetration loss (PL) 0 dB 0 dB(outdoor) Log-normal fading 0 dB 0
dB(outdoor) margin(LF) PL model(L(d))[dB] Okumura-Hata LMDS channel
model (Suburban areas) (Good, Bad) + Margin w.r.t height Target
coverage(d)[km] About 14 km 3 km(RTT = 19.8 us)
[0094] The target area of the sequence is finally verified by
[Equation 11].
T SEQ = N 0 N f P RA ( d ) E P N 0 [ Equation 11 ] ##EQU00012##
[0095] [Equation 11] is expressed as a function of distance d by
which an appropriate effective distance may be estimated. A
verification example regarding an LTE case and a high carrier
frequency case with a service coverage of 3 km and a TTI of 222
.mu.s will be described below. It is assumed that the maximum
channel delay spread is 0.5 .mu.s.
[0096] A path loss function P.sub.RA(d) in [Equation 11] may be
represented as [Equation 12], in terms of dB.
P.sub.RA(d)=P.sub.max+G.sub..alpha.-L(d)-LF-PL(dB) [Equation
12]
[0097] A substantial path loss is expressed as a function L(d) in
[Equation 12]. An Okumura-Hata model applies in designing an RACH
in the LTE system.
[0098] FIG. 10 is a graph illustrating RACH sequence length versus
service coverage in the LTE system. Particularly, a suburban
situation of the Okumura-Hata model is taken in FIG. 10. Referring
to FIG. 10, it is noted that if a BS height is 60 m at a point
where the sequence length T.sub.SEQ is1 ms, the service coverage is
about 14 km.
[0099] For verification in the high carrier frequency case, a Local
Multipoint Distribution. Services (LMDS) model applies to the path
loss function L(d) . FIG. 11 is a graph illustrating RACH sequence
length versus service coverage in the high carrier frequency
system. Referring to FIG. 11, it is noted that a service coverage
with a sequence length T.sub.SEQ of 111.3 .mu.s is appropriately 14
km, far larger than a target coverage of 3 km.
[0100] As described above, an RACH transmission period may vary
with a service coverage and a TTI. In addition, to maintain
orthogonality with an existing OFDM frame, an RACH subcarrier
spacing should be an integer multiple of an existing subcarrier
spacing. This means that the RACH subcarrier spacing gets shorter
in the frequency domain and an RACH OFDM symbol having a longer
period than an existing OFDM symbol period is set in the time
domain. That is, an RACH OFDM symbol is designed to be k times
longer than an existing OFDM symbol based on the relationship that
.DELTA..sub.RA=.DELTA.f/k.
[0101] In the present invention, an RACH sequence length is
determined based on the relationship between an OFDM symbol period
and an RACH OFDM symbol period.
[0102] In this specification, a method of determining an RACH
effective sequence length when an RACH transmission band of a UE is
given is described. In consideration of amplifier power of the UE,
it is most possible to basically transmit the RACH in a partial
band smaller than a frequency band of an overall system. In
addition, a subcarrier spacing of the RACH is smaller than that of
a general data channel (that is, .DELTA..sub.RA=.DELTA.f/k) and
thus an RACH symbol having a longer period may be transmitted in
the time domain.
[0103] In the present invention, when the RACH transmission band of
the UE is given, a final effective sequence length is determined by
sequentially considering the following factors. Specifically, a
method for design of an RACH for substantial high carrier frequency
transmission will be described in detail with regard to an example
considering center frequency-based path loss models for high
carrier frequency band transmission. [0104] Reference signal to
noise ratio of RACH channel [0105] Reference signal to noise ratio
of data channel [0106] Path loss model (general cellular band and
high carrier frequency band (>10 GHz)) [0107] RACH reception
request signal to noise ratio of BS [0108] RACH transmission band
[0109] Sequence type (Poly-phase sequence and m-sequence)
[0110] 1. Method for Determining RACH Preamble Sequence Length
[0111] Basically, an RACH is managed in unsynchronization with
uplink and thus is detected based on correlation characteristics of
sequences without channel estimation. Timing advance (TA) may also
be managed based on this correlation.
[0112] With regard to an RACH sequence managed according to the
correlation characteristics, a sequence with excellent
autocorrelation characteristics or excellent cross correlation
characteristics may be selected and applied according to its
interference characteristics. In general, when intra-cell
interference is low, it is advantageous to use a poly-phase
sequence with excellent autocorrelation characteristics, such as a
Zadoff-Chu (ZC) sequence. When intra-cell interference is high, it
is advantageous to use an m-sequence such as a pseudo-random
sequence.
[0113] In general, on the assumption that an RACH preamble uses
lower transmission power than general data, summation of
transmission power is used via increase in sequence length in order
to increase RACH detection accuracy due to the low transmission
power. Thus, signal to noise ratio (SNR) compensation using a
sequence length is calculated according to [Equation 13] below and
is defined as an adjusting value. For example, when a sequence
length is 1,000, an adjusting value is 30 dB, and it may be deemed
that an RACH signal SNR, which is actually detected by a UE,
increases by about 30 dB.
Adjusting Value=10 log.sub.10(SequenceLength) [Equation 13 ]
[0114] As a result, when the RACH sequence length is set, the RACH
sequence length may vary according to requirements for restricting
a range of the adjusting value to a predetermined region. In
general, E.sub.p/N.sub.0 that is an actual SNR of the RACH is given
as a relative value. That is, it is assumed that the UE transmits
an RACH signal with a lower specific value having DB as a unit,
than E.sub.s/N.sub.0 as an SNR of a data transmission signal
detected by the BS from the UE at a target position. In general, it
is assumed that E.sub.p/N.sub.0 is lower than E.sub.s/N.sub.0 by 24
dB. In other words, this means that it is assumed that
E.sub.p/N.sub.0=E.sub.s/N.sub.0-24 dB.
[0115] Hereinafter, on the aforementioned assumption, processes of
calculating the RACH sequence length will be sequentially
described.
[0116] (1) First Step: Calculation of Path Loss Based on Reference
Point of UE
[0117] First, in order to calculate path loss, when the UE
transmits a signal with maximum transmission power at a specific
distance from the BS, path loss measured in the BS needs to be
preferentially calculated. In general, a path loss function
P.sub.s(d) is represented according to [Equation 14] below. Here,
actual path loss is L(d) and other parameters may be given as
follows.
P s ( d ) = P max + G a - L ( d ) - LF - PL ( dB ) { P max ( Tx
Power ) = 24 dBm = - 6 dB G a ( Rx Ant Gain ) = 15 dBi LF (
Shadowing ) = 0 dB PL ( PenetrationLoss ) = 0 dB L ( d ) : Path -
Loss [ Equation 14 ] ##EQU00013##
[0118] For example, the LTE case assumes an RACH with d=0.68 km and
calculates path loss using the Okumura-Hata path loss model. The
high carrier frequency case assumes an LDMS model represented by
[Equation 15] below and a distance d=0.3 km. In both the cases,
other parameters are shown in [Table 6] above.
P.sub.s(d)=P.sub.max+G.sub..alpha.-32.44-20
log.sub.10(f.sub.c,GHzd.sub.m)-L.sub.exv{L.sub.env=15 db [Equation
15]
[0119] In this case, path loss in a data signal received by the BS
is 123.8 dB in the LTE case and 118.5 dB in the high carrier
frequency case due to different amplitudes of center frequencies
and different path loss models.
[0120] (2) Second Step: Calculation of Amplitude of Noise Signal
According to RACH Allocation Band
[0121] In general, a final value may be calculated according to a
transmission band of an RACH on the assumption of noise as
N.sub.0(=-174 dBm/Hz). For example, it is assumed that the RACH is
allocated to 1.08 MHz in the LTE case and 5 MHz in the high carrier
frequency case. In this case, the amplitudes of noise signals are
calculated according to [Equations 16] below.
N.sub.0.108 MHz=-204 dB+10 log.sub.10(1.08 MHz)=-143.7
dB-LTEcase
N.sub.0.5 MHz=-204 dB+10 log.sub.10(5 MHz)=-137 dB-High carrier
frequencycase [Equation 16]
[0122] (3) Third Step: Calculation of Reference E.sub.s/N.sub.0 for
General Data Transmission
[0123] A final E.sub.s/N.sub.0 is calculated according to [Equation
17] below. In this case, since the path loss and the noise signal
amplitude are calculated in the first and second steps, the noise
figure of a receiver is lastly considered.
E s N 0 = P s ( d ) N 0 N f = P s ( d ) - N f - N 0 ( dB ) [
Equation 17 ] ##EQU00014##
[0124] For example, on the assumption of N.sub.f=5 dB,
E.sub.s/N.sub.0 of each of the LTE case and the high carrier
frequency case may be represented according to [Equation 18]
below.
E s N 0 = P s ( d ) - N f - N 0 = - 123.8 - 5 - ( - 143.7 ) = 14.9
dB - LTE case E s N 0 = P s ( d ) - N f - N 0 = - 118.5 - 5 + 137 =
13.5 dB - High carrier frequency case [ Equation 18 ]
##EQU00015##
[0125] (4) Fourth Step; Calculation of Final E.sub.p/N.sub.0 of
RACH
[0126] In a fourth step, it is assumed that an RACH reception
signal to noise ratio is lower than a data reception signal to
noise by about 24 dB. For example, the LTE case and the high
carrier frequency case of [Table 6] acquire E.sub.p/N.sub.0
according to [Equation 19] below.
E p N 0 = E s N 0 - 24 dB = 14.9 - 24 = - 9.1 dB - LTE case E p N 0
= E s N 0 - 24 dB = 13.5 - 24 = - 10.5 dB - High carrier frequency
case [ Equation 19 ] ##EQU00016##
[0127] (5) Fifth Step: Calculation of Required RACH Sequence Length
to Satisfy E.sub.p/N.sub.0
[0128] As described above, SNR compensation using the RACH sequence
length is possible, which is achieved using sequence energy
summation based on correlation. Thus, lastly, a value satisfying
[Equation 20] below may be acquired. That is, an adjusting RACH
sequence length for satisfying E.sub.p/N.sub.0 calculated in the
fourth step may be calculated.
Required E p N 0 = E P N 0 + 10 log 10 ( SequenceLength ) [
Equation 20 ] ##EQU00017##
[0129] In reality, in the LTE case, the RACH sequence length is
calculated on the assumption of E.sub.p/N.sub.0=-11 dB and Required
E.sub.p/N.sub.0=18 dB, and in the high carrier frequency case, the
RACH sequence length is calculated on the assumption of the
aforementioned E.sub.p/N.sub.0=-10.5 dB. In this case, the RACH
sequence length is 839 in the LTE case and 707.9 in the high
carrier frequency case.
[0130] (6) Sixth Step: Determination of Final Sequence Length
[0131] Basically, in order to satisfy the adjusting value, the same
or larger value than the calculated required sequence length is
needed. However, one factor needs to be additionally considered. An
RACH and a general data channel have different subcarrier intervals
and thus guard bands need to be allocated to opposite ends of a
frequency band, to which the RACH channel is allocated, in order to
ensure the orthogonality between the RACH and the data channel.
[0132] FIG. 12 illustrates the concept of an RACH allocated to a
partial band and configuration of guard bands.
[0133] Referring to FIG. 12, the orthogonality between two channels
is ensured by configuring guard bands at subcarrier intervals of
data channels. Accordingly, [Equation 21] below needs to be
satisfied.
SequenceLength + 2 .times. k .ltoreq. BW RA / ( .DELTA. f / .DELTA.
f RA ) { k = .DELTA. f .DELTA. f RA [ Equation 21 ]
##EQU00018##
[0134] In [Equation 21] above, k refers to a guard band. In the LTE
case, a ZC sequence is used for RACH design, the guard band is set
as 31.25 kHz>2.DELTA.f. and a final sequence length is 839 that
is a prime number.
[0135] As another example, in the high carrier frequency case, the
required sequence length calculated in the fifth step needs to be
707.9 or more. Accordingly a final value is calculated according to
[Equation 22] below. Here, an RACH transmission band is assumed as
5 MHz.
SequenceLength+2.times.k.ltoreq..left
brkt-bot.BW.sub.RA/(.DELTA.f/.DELTA.f.sub.RA).right brkt-bot.=828
[Equation 22]
[0136] A last factor to be considered to determine the last
adjusting value is a sequence type. For example, when the RACH
sequence is a ZC sequence, a prime number satisfying `Max prime
number.ltoreq.sequence-length` is selected. In addition, when the
RACH sequence is a PN sequence, the calculated sequence length can
be used.
[0137] Accordingly, in the high carrier frequency case, since a
largest prime number among prime numbers satisfying a sequence
length, 828 is 827, the sequence is 827 in case of the ZC sequence,
and is 828 in case of the PN sequence.
[0138] 2. Method of Configuring Zero-Correlation Zone of RACH
Sequence in Consideration of Characteristics of High Carrier
Frequency
[0139] In the LTE system, a subcarrier interval .DELTA.f.sub.RA of
an RACH is set to be about 1/12 times lower than a subcarrier
interval .DELTA.f of an existing data channel when an RACH sequence
is designed. Accordingly, lastly, in the LTE system, a basic
subcarrier interval satisfies .DELTA.f=15 kHz and
.DELTA.f.sub.RA=1.25 kHz.
[0140] In the high carrier frequency system, when a subcarrier
interval is set to be smaller than a basic subcarrier interval,
influence on a Doppler's frequency may be further increased
degrading detection performance. For example, in the high carrier
frequency case using 30 GHz as a center frequency, a UE with the
same movement speed may lead to a Doppler effect 15 times higher
than a case of 30 GHz. Accordingly, in the RACH for a high carrier
frequency band, when an amplitude of .DELTA.f.sub.RA is reduced as
in the legacy LTE, performance may be greatly degraded.
[0141] In general, as an amplitude of .DELTA.f.sub.RA is reduced,
the number of channel taps corresponding to an effective channel is
one. Thus, on the assumption that the number of effective multiple
paths of a channel is one, a BS may measure correlation between
RACH sequences transmitted from UEs to identify each UE or estimate
timing difference.
[0142] However, the RACH subcarrier interval needs to be the same
as the basic subcarrier interval in consideration of the Doppler
effect of a high carrier frequency channel, and thus, the channel
tap of the effective channel cannot be assumed as a single tap,
which will be described with reference to drawings.
[0143] FIG. 13 illustrates the concept of an effective single path
due to small .DELTA.f.sub.RA and sequence reception of a BS. FIG.
14 illustrates the concept of an effective single path due to great
.DELTA.f.sub.RA and sequence reception of a BS.
[0144] As illustrated in FIG. 13, when an RACH with a relatively
small subcarrier interval .DELTA.f.sub.RA transmits ZC sequences
s.sub.0, s.sub.1, s.sub.2, s.sub.3, . . . , s.sub.N-1, the length
of a transmission symbol is increased on the time axis, and thus,
an effective channel section is assumed to be a single tap.
However, as illustrated in FIG. 14, when an RACH with a relatively
great subcarrier interval .DELTA.f.sub.RA transmits ZC sequences
s.sub.0, s.sub.1, s.sub.2, s.sub.3, . . . , s.sub.N-1, the length
of a transmission symbol is reduced on the time axis, and thus, an
effective channel section is shown as a multiple path. Accordingly,
correlation between sequences needs to be performed by as much as
overlap between each sequence sample section of the RACH and L
multiple paths.
[0145] It may be ensured that a first channel tap h.sub.0 of the
multiple paths is selected. That is, h.sub.1, h.sub.2, h.sub.3, . .
. , h.sub.L-1 may be selected, which may lead to reduction in
performance when a value for timing advance (TA) of uplink is
accurately estimated. Thus, the present invention proposes
configuration of a zero-cross correlation zone of each UE when an
RACH for a high carrier frequency is designed.
[0146] (A) First, configuration of a zero-cross correlation zone of
a ZC sequence in consideration of an RACH subcarrier interval and a
maximum delay profile may be considered.
[0147] That is, when maximum channel time of a channel is
.tau..sub.Max, time axis samples may be formed by as much as the
number obtained by dividing .tau..sub.Max by a sampling time, and
an RACH sequence may be received by the BS through multiple path
channels, the number of which corresponds to the time axis samples.
The ZC sequence is represented according to [Equation 23]
below.
s u ( n ) = - j .pi. un ( n + 1 ) N , 0 .ltoreq. n .ltoreq. N - 1 (
N = SequenceLength ) [ Equation 23 ] ##EQU00019##
[0148] In Equation 23 below, u refers to a root value and N refers
to a sequence length.
[0149] In this case, cyclic shift corresponding to a specific
length may be used to allocate a sequence to multiple users, which
may be used to identify various users using one sequence or to
perform timing advance (TA). This will be described with reference
to drawings.
[0150] FIG. 15 illustrates a cyclic shift principle using a ZC
sequence. FIG. 16 illustrates the concept of allocation of a
multiple user sequence using cyclic shift. FIG. 17 illustrates an
example of user detection in different zero-correlation zones.
[0151] As illustrated in FIG. 15, despite the same ZC sequence, the
ZC sequence is orthogonal to a cyclically-shifted sequence. Thus,
as illustrated in FIG. 16, when a cyclic shift section is divided
and allocated to users, a BS may measure correlation between ZC
sequences received at the same time to differentiate UEs or to
estimate a delay point. Thus, as illustrated in FIG. 17, different
zero-correlation zones may be configured to detect users.
[0152] Hereinafter, consideration of the RACH subcarrier interval
.DELTA.f.sub.RA due to high carrier frequency characteristics and a
maximum delay time .tau..sub.Max when the zero-correlation zone is
configured using the aforementioned ZC sequence will be
described.
[0153] First, the number L of samples of an effective channel
section for configuration of the zero-correlation zone is
calculated according to [Equation 24] below. That is, the number L
of samples of the effective channel section is calculated to
prevent the risk of detecting another signal of a user, formed by
receiving a signal of a specific user via channel delay.
L = .tau. Max t s = .tau. Max .DELTA. f RA N FFT or L = .tau. Max t
s = .tau. Max .DELTA. f RA N FFT N FFT : FFT size [ Equation 24 ]
##EQU00020##
[0154] In [Equation 24] above, the zero-correlation zone is
increased by as much as L that is the calculated number of samples
of an effective channel. Thus, although a total number of users
that can be identified via the same ZC sequence is reduced, the
accuracy of user detection may be improved.
[0155] When an entire sequence length N is divided by a cyclic
shift length N.sub.cs, a total number of users may be calculated
according to [Equation 25] below by applying L that is calculated
via the aforementioned process.
No . of users = N L + N CS [ Equation 25 ] ##EQU00021##
[0156] In this case, a zero-correlation zone of a final ZC sequence
is allocated according to [Equation 23] and [Equation 25] above.
FIG. 18 illustrates an example of configuration of a
zero-correlation zone in consideration of an effective channel
section L according to an embodiment of the present invention.
[0157] As seen from FIG. 18, a point of time when a UE actually
transmits a sequence is determined using only the number L of
samples of the effective channel section of a total length
L+N.sub.CS, and a point of time for reception of a signal varies
according to a position of the UE within the same value
N.sub.CS.
[0158] Even if UEs simultaneously transmits sequences, the
sequences may be received at different points of time according to
positions of the UE and BS, which will be described with reference
to the drawings.
[0159] FIG. 19 illustrates sequence overlapping that occurs when an
effective channel section L is not considered. In addition, FIG. 20
illustrates an example of configuration of zero-correlation zone
where sequence overlapping does not occur in consideration of the
effective channel section L. In particular, in FIGS. 19 and 20, it
is assumed that a total sequence length N is 18 and a
zero-correlation zone of each user is 6, and that the number of L
of samples of an effective channel section according to channel
delay is 3. In addition, it is assumed that a UE #1 using a
zero-correlation zone #1 is close to a BS such that an RACH
sequence reaches the BS at initial delay .tau..sub.0=0 s.
[0160] When the number L of samples of the effective channel
section is not considered, on the assumption that a sequence
extremely reaches a UE #2 using a zero-correlation zone #2 at a
last point of time of zero-correlation, a reception sequence of the
UE #1 and the UE #2 is shown in FIG. 19. Thus, sequence overlapping
degrades performance according to effective channel path delay,
reducing sequence detection accuracy. On the other hand, it can be
seen that, although the available cyclic shift number of a sequence
configured with L+N.sub.ZC=9 is 2 that is smaller than 3 shown in
FIG. 19, an overlapping region of the sequence is not present to
increase detection accuracy, as illustrated in FIG. 20.
[0161] (B) Next, a method for configuring a zero-correlation zone
of a ZC sequence in consideration of only a partial region of
channel delay and a subcarrier interval of an RACH may be
considered.
[0162] The aforementioned (A) describes a method for configuring a
zero-correlation zone in consideration of all channel effective
delay times. However, hereinafter, the present invention suggests a
method for reflecting some of channel effective delay times. It is
advantageous in that, when some of the channel effective delay
times are reflected, the number of users that can be supported by
the same sequence may be increased, compared with a case in which
cyclic shift corresponding to the number L of samples of the
effective channel section is not used.
[0163] i) First, various RACH formats to which different effective
channel lengths are reflected may be configured, and a BS may
indicate an RACH format that can be used by a UE via signaling.
[0164] When the BS defines various formats of RACH sequences and
reception RACH delay of a user according to coverage of the user in
a cell is extremely increased, UEs are notified of RACH formats to
which the number L of samples of a maximum effective channel
section is applied. In addition, when delay of an RACH received by
the BS is equal to or less than a specific reference, RACH delay in
consideration of only a portion of the number of samples of the
effective channel section may be used.
[0165] [Table 7] below shows examples of configuring RACH formats
for the number L of samples of effective channel sections. In
detail, when timing advance (TA) or a reception delay point
estimated by each UE is equal to or more than a reference value,
Format #1 is used and, otherwise, Format #2 is used. Here, it can
be seen that the number of users that can be supported by Format #2
is increased compared with users that can be supported by Format
#1.
TABLE-US-00007 TABLE 7 Basic Zero- Final Zero- correlation
correlation No. of Format zone length zone length available UEs #1
N.sub.ZC L + N.sub.ZC N L + N ZC ##EQU00022## #2 N.sub.ZC L/2 +
N.sub.ZC N L / 2 + N ZC ##EQU00023## . . . . . . . . . . . .
[0166] ii) Alternatively, an initial access UE may use an RACH
format to which a longest effective channel length, that is, the
number of samples of the effective channel section is reflected and
then a format with a smaller number of samples of the effective
channel section than L may be allocated.
[0167] In detail, the initial access user may use Format #1 of
formats of Table 7 above and then receive signaling of the BS and
use another format. The RACH is a channel that is periodically
transmitted to the BS from the UE for an operation such as TA in
addition to initial access of the UE, and thus, more
zero-correlation zones may be configured using the same sequence so
as to increase the number of users supported.
[0168] Needless to say, when an overlapping or ambiguous region of
the zero-correlation zone is not present, an objective can be
achieved by configuring a portion of the same sequence region as
the zero-correlation zone of Format #1 and configuring another
portion as the zero-correlation zone of #2. FIG. 21 illustrates an
example in which the same ZC sequence is designed in Format #1 and
Format #2.
[0169] The present invention proposes a method of designing an
effective sequence length for an RACH appropriate for a
communication environment using a high carrier frequency band. In
particular, a high carrier frequency band has high path loss due to
a high center frequency and thus it is appropriate to apply the
high carrier frequency band to a small cell. However, the present
invention is not limited thereto.
[0170] FIG. 22 is a block diagram of a communication apparatus
according to an embodiment of the present invention.
[0171] Referring to FIG. 22, a communication apparatus 2200
includes a processor 2210, a memory 2220, a Radio Frequency (RF)
module 2230, a display module 2240, and a User Interface (UI)
module 2250.
[0172] The communication device 2200 is shown as having the
configuration illustrated in FIG. 22, for the convenience of
description. Some modules may be added to or omitted from the
communication apparatus 2200. In addition, a module of the
communication apparatus 2200 may be divided into more modules. The
processor 2210 is configured to perform operations according to the
embodiments of the present invention described before with
reference to the drawings. Specifically, for detailed operations of
the processor 2210, the descriptions of FIGS. 1 to 21 may be
referred to.
[0173] The memory 2220 is connected to the processor 2210 and
stores an Operating System (OS), applications, program codes, data,
etc. The RF module 2230, which is connected to the processor 2210,
upconverts a baseband signal to an RF signal or downconverts an RF
signal to a baseband signal. For this purpose, the RF module 2230
performs digital-to-analog conversion, amplification, filtering,
and frequency upconversion or performs these processes reversely.
The display module 2240 is connected to the processor 2210 and
displays various types of information. The display module 2240 may
be configured as, not limited to, a known component such as a
Liquid Crystal Display (LCD), a Light Emitting Diode (LED) display,
and an Organic Light Emitting Diode (OLED) display. The UI module
2250 is connected to the processor 2210 and may be configured with
a combination of known user interfaces such as a keypad, a touch
screen, etc.
[0174] The embodiments of the present invention described above are
combinations of elements and features of the present invention. The
elements or features may be considered selective unless otherwise
mentioned. Each element or feature may be practiced without being
combined with other elements or features. Further, an embodiment of
the present invention may be constructed by combining parts of the
elements and/or features. Operation orders described in embodiments
of the present invention may be rearranged. Some constructions of
any one embodiment may be included in another embodiment and may be
replaced with corresponding constructions of another embodiment. It
is obvious to those skilled in the art that claims that are not
explicitly cited in each other in the appended claims may be
presented in combination as an embodiment of the present invention
or included as a new claim by a subsequent amendment after the
application is filed.
[0175] The embodiments of the present invention may be achieved by
various means, for example, hardware, firmware, software, or a
combination thereof. In a hardware configuration, the methods
according to exemplary embodiments of the present invention may be
achieved by one or more Application Specific Integrated Circuits
(ASICs), Digital Signal Processors (DSPs), Digital Signal
Processing Devices (DSPDs), Programmable Logic Devices (PLDs),
Field Programmable Gate Arrays (FPGAs), processors, controllers,
microcontrollers, microprocessors, etc.
[0176] In a firmware or software configuration, an embodiment of
the present invention may be implemented in the form of a module, a
procedure, a function, etc. Software code may be stored in a memory
unit and executed by a processor. The memory unit is located at the
interior or exterior of the processor and may transmit and receive
data to and from the processor via various known means.
[0177] Those skilled in the art will appreciate that the present
invention may be carried out in other specific ways than those set
forth herein without departing from the spirit and essential
characteristics of the present invention. The above embodiments are
therefore to be construed in all aspects as illustrative and not
restrictive. The scope of the invention should be determined by the
appended claims and their legal equivalents, not by the above
description, and all changes coming within the meaning and
equivalency range of the appended claims are intended to be
embraced therein.
INDUSTRIAL APPLICABILITY
[0178] Although an example of applying a method and apparatus for
configuring a random access sequence length for a high carrier
frequency band in a wireless communication system to a 3.sup.rd
generation partnership project (3GPP) long term evolution (LTE)
system has been described, the present invention is applicable to
various wireless communication systems in addition to the 3GPP LTE
system.
* * * * *